The present invention relates to a method of working a recessed portion in a headrest stay which is installed on an upper end of a seatback of an automotive vehicle, as well as a press apparatus for working a recessed portion in a headrest stay.
A headrest S installed on an upper end of a seatback of an automobile or the like is provided with a plurality of recessed portions 2 for height adjustment in a stay portion 32 of a headrest stay 3 at predetermined intervals (FIGS. 14 and 15). In the drawings, reference numeral 2a denotes a recessed portion for preventing the headrest from coming off; 2b, a retaining recessed portion; 31, an insert portion; and P, a pillow portion. In recent years, for the purpose of lightweight a pipe is extensively used as the headrest stay 3 which is built into the headrest S. These recessed portions 2 have hitherto been formed by such as (1) a cutting method including milling and broaching and (2) a method based on press working.
However, the recessed portions of the stay for the headrest using a pipe as its basic material function to adjust and hold the vertical position of the headrest, and have naturally been required to satisfy predetermined strength. In the case where the recessed portions are worked by the cutting method (1), it has been necessary to use a thick-walled pipe so that even those portions where the wall thickness is smallest would be able to maintain the predetermined strength (FIG. 16A). Also in a case where those portions that are to be recessed by milling or broaching are subjected in advance to preliminary recessing, it has been necessary to secure the predetermined thickness at the portions where the wall thickness is smallest (FIG. 16B).
Meanwhile, in the case where recessed portions are formed by being removed by press working in the method (2), large burrs occur due to the wear and the like of a punch, incurring cost in their grinding (FIG. 16C). Further, fractured surfaces are rugged, and it has been difficult to obtain sharp edges necessary as the function of the recessed portions. In addition, with the method in which the pipe is held by a die and is merely pressed in from above by a punch, it has been difficult to form sharp shapes owing to the characteristics of the pipe. As a result, edge rounding has occurred, as shown in FIG. 16D. Hence, there has been a drawback in that the stopper function cannot be demonstrated due to the edge rounding in press working, causing the headrest to come off the upper end of the seatback.